Study On Molecular Mechanism Of Red Light-mediated Agravitropism In Arabidopsis

Plants have a special adaptability to gravity.Root will grow downwards towards the direction of gravity.It is positive gravitropism.Stem will grow in the opposite direction.It is the negative gravitropism of the stem.Studies have found that hypocotyl in Arabidopsis thaliana grow in random orientations under red light.It is referred to inhibit hypocotyl negative gravitropism.Light is involved in regulating gravity signal transduction,such as phytochromes、PIFs(PHYTOCHROMEINTERACTING FACTORs)、HY5(ELONGATED HYPOCOTYL5).In order to further explore the molecular mechanism of phytochrome-mediated agravitropism under red light,this project include the following aspects.1.The role and regulation of COP1:This study found that the COP1 mutant has hypocotyl agravitropism in dark.cop1 lacks amyloplast observed in starch staining.COP1 control the expression of RPGE1(REPRESSOR OF PHOTOSYNTHETIC GENES1)and LAZY4(the gravity signal gene).It is proved that COP1 is involved in regulating the hypocotyl negative gravitropism.In addition,We found that COP1 locates in the nucleus and forms nuclear speckles under dark conditions.White light treatment may reduce the level of COP1 in the nucleus,but red light may not.In general,The differential regulation of COP 1 localization by red and white light may be the reason that seedlings exhibit different gravitropism.2.The molecular mechanism is about regulating exoression of LAZY4 in hypocotyls.Yang proposed that red light treatment can negatively regulate the negative gravitropism by disrupting the expression of LAZY4 in the hypocotyl.We reported that white and red light treatment inhibit the expression of LAZY4 in hypocotyls in short-term.There are differential expression patterns in red light and white light in long term,which may be one of the reasons for agravitropism in red light.In dark to light,the protein level of HY5 becomes higher,but HY5 level in white lingt is more than in red light.Then,the protein level of PIF4 becomes less in dark to loight.But PIF4 level in red light is less than in white light.HY5 and PIF4 control the expression of LAZY4 in hypocotyls,to regulate gravitropism.3.Microtubules may be involved in regulating the gravitropism.In this study,sav2(shade avoidance 2)was used to observe the phenotype and sav2 inhibit hypocotyl negative gravitropism.Using PPM and Taxol affects the stability of microtubules,and hypocotyl presented direction randomization.And the distribution of microtubules regulate gravitropism.Liu reported that WDL3 regulates microtubule dynamics;COP1 interact with WDL3 under dark in order to promote the degradation of WDL3.We found that knocking down the expression of WDL3 can partially restore the lodging phenotype of cop1 in dark;under red light conditions,WDL3 cannot accumulate,wihch is similar to that under dark;This result is consistent with the change pattern of COP1 subcellular localization in nucleus.We speculate that WDL3 and COP1 are involved in regulating negative gravitropism through affecting the microtubules.